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finite-differences.go
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finite-differences.go
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package main
import (
"bufio"
"flag"
"fmt"
"io"
"os"
)
var (
status = 0
order = flag.Uint("n", 4, "calculate differences to nth order")
)
func main() {
flag.Usage = usage
flag.Parse()
if flag.NArg() < 1 {
diff(bufio.NewReader(os.Stdin))
} else {
for _, name := range flag.Args() {
f, err := os.Open(name)
if ek(err) {
continue
}
diff(bufio.NewReader(f))
f.Close()
}
}
os.Exit(status)
}
func usage() {
fmt.Fprintln(os.Stderr, "usage: finite-differences [options]")
flag.PrintDefaults()
os.Exit(2)
}
func ek(err error) bool {
if err != nil {
fmt.Fprintln(os.Stderr, "finite-differences:", err)
status = 1
return true
}
return false
}
func diff(r io.Reader) {
p := make([][]float64, *order+1)
for {
var v float64
_, err := fmt.Fscan(r, &v)
if err != nil {
break
}
p[0] = append(p[0], v)
}
for i := uint(1); i <= *order; i++ {
for j := 0; j < len(p[i-1])-1; j++ {
p[i] = append(p[i], p[i-1][j+1]-p[i-1][j])
}
}
for i := range p {
fmt.Printf("%10v ", i)
}
fmt.Printf("\n\n")
for i := range p[0] {
for j := range p {
if i >= len(p[j]) {
fmt.Printf("%10.2f", 0.0)
} else {
fmt.Printf("%10.2f", p[j][i])
}
fmt.Printf(" ")
}
fmt.Printf("\n")
}
}